Prior to the present invention, a method for making bisimides was shown by Markezich et al, "Reactions of Fluoride and Nitrite Ions with 4-Nitrophthalimides", Journal of Organic Chemistry, 42, 3431 (1977), involving reactions of 4-nitro-N-methylphthalimide with either fluoride or nitrite salts in a dipolar aprotic solvent, affording up to a 78% yield of the corresponding diarylether, 4,4'-oxybis(N-methylphthalimide). Although high yields of diarylether can be obtained utilizing certain alkali nitrite salts or alkali fluoride salts, reaction times of 18-20 hours are often required.
In Jones et al, U.S. Pat. No. 4,558,164, a method for making symmetrical dinitrodiphenyl ethers is shown using halonitrobenzenes and a mixture of potassium acetate and potassium carbonate. However, side reactions have been found to occur in the Jones et al method rendering this procedure unsuitable for ether bisimide formation.
The present invention is based on my discovery that nitrophthalimides of the formula, ##STR1## where R is a C.sub.(1-14) monovalent organic radical, can be converted to the corresponding bisimide of the formula ##STR2## with yields as high as 80% and reaction time as little as 7.5 hours, by heating the nitrophthalimide in the presence of a dipolar aprotic solvent and an effective amount of alkali metal carboxylate.